Separation of oil and wax



Dec, 7, 1954 B. c. BEQNEDICT, JR 2,696,459

SEPARATION OF OIL AND wAx Filed June 7, 1951 l8 SOLVENT l4\ WAX 2|\ W CHILLER WASHING FILTER I TANK CRUDE WAX I I 1 OILL SLURRY OIL\ lLLER cI-I TANK FILTER 7f INVENTOR.

B. C. BENEDICT Ia A 7' TORNE VS United States Patent SEPARATION OF OIL AND WAX Bruce C. Benedict, Jr., Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Application June 7, 1951, Serial No. 230,322

11 Claims. (Cl. 196-18) This invention relates to deoiling of wax.

In one method described in the art wax is crystallized from a wax-oil solution by cooling the solution with slow agitation in the absence of a solvent or in the presence of a very limited proportion of a solvent to a temperature low enough to crystallize a portion of the wax and then the thus formed wax-oil mass is commingled with a cooled solvent and subjected to a filtering operation to separate the crystallized wax.

In the practice of the prior art process in which a San Roque, Venezuela, wax-oil fraction. boiling range 750 850 F., with a viscosity of 38.25 SUS at 210 F., which will be recognized to be low enough to not require solvent ordinarily, was to be deoiled it was found that the fraction could not be slowly cooled with slow agitation without the formation of large wax lumps. A to inch in diameter. These wax lumps were formed from the higher melting point waxes which crystallized out of solution at the relativelv high temperatureof 110 F. Lump formation is hi hly undesirable for two reasons. First, the lumps occlude oil with the result that the wax is not deoiled. Second, the lumps cause operating difi'iculties by plugging lines and eouipment. This lump f rmation was unexuected,.especially so, because the oil still had a sufficiently low viscositv to be effectively stirred and chilled. Furthermore, this lump formation occurs only with certain oils. To date. the only oil encountered with exhibits lumn formation is the San Roque, Venezuela, wax-oil frac ion referred to above. Thus. the usual reason for adding solvent, namely, high viscosity, did not exist when the wax lumps were formed.

I have discovered that this lump formation can be completely eliminated by the addition of at least one volume of solvent to ten vol mes of the oil fraction. preferably five volumes of the oil fraction, while all of the wax is in solution and then co ling the mixture. The mixture then processes satisfact rilv. that is, without the formation of wax lumps, and with high filter rates and produces waxes with a low oil content. This process is applicable to a waxy distillate having a boiling range 650 to 950 F. and con aini g 20 to 50 per cent wax.

Therefore according to this invention there is provided a meth d for deoilin a wax-oil solution or mixture. boiling in the range 650950 F. and containing 20 to 50 per cent removable wax, which wax exhibits lump formation when deoiled by conventional methods, by adding to said mixture, while the wax is still in solution, at least as much as one volume of solvent to ten volumes of wax-oil fraction and then cooling the mixture with slow agitation.

The preferred solvent is a naphtha fraction having a boiling ran e from 200 to 400 F., more preferably 300 to 400 F. The naphtha fraction may be obtained from the original crude oil.

Figure 1 illustrates diagrammatically a method of practice of the invention.

Oil stock from conduit is first mixed with solvent from conduit 11 in the chiller 12. The oil stock is a distillate fraction having a boiling range of 700 to 950 F. with a wax content of to 50 per cent. The mixing operation takes place at a temperature sufiiciently high to effect solution of all the oil and wax constituents of the stock in the solvent. Preferably, only a portion of the solvent is added, about one gallon of solvent to 5 gallons of oil stock. In the case of dilution with naphtha, the temperature is usually 120 F. or higher. The mixture is then cooled slowly in the chiller 12 to the filtering temperature, usually 50 F. The mixture is passed to a slurry tank 13.

Solvent from conduit 11 cooled to 50 F. in chiller 14 is pumped into the slurry tank 13 and thoroughly mixed with the oil-wax-solvent mixture. The mixture is passed to a filter 15 wherein the mixture is separated into a crude wax phase passed into conduit 16 and a wax-free oil phase passed into conduit 17.

The oil obtained from the filter is distilled in order that the solvent which it contains may be recovered and reused in the dilution of further oil to be dewaxed. The crude wax cake may be transferred back to the slurry tank 13 (step not shown) or to a wax washing tank 18. The wax is washed with the solvent and refiltered for a total of about three times to obtain a purified wax at 19. The purified wax cake will contain less than 0.5 weight per cent of oil and is very light in color so that the wax percolated through bauxite at 180 F. to a yield of 25 barrels of wax per ton of bauxite produced a finished wax with very good color stability.

A wax distillate fraction boiling substantially between 700 to 850 F. at atmospheric pressure obtained by conventional means of steam distillation in a packed column from a San Roque, Venezuela, crude oil was mixed with a Stoddard Solvent (a naphtha boiling in the range 300- 400 F.) in the ratio of five volumes oil stock to one volume of solvent at a temperature of F. This solution was passed through chiller 12 and slurry tank 13 chilled at the rate of 1 F. per minute to effect precipitation of wax. The final temperature of the chilled wax was 50 F. Additional solvent was added to the slurry tank, and the mixture was passed through the filter 15 to effect separation of wax from the oil. Additional solvent was charged to the filter as a wash spray. Addition of up to 0.5 volume of solvent per volume of wax distillate prior to chilling did not adversely affect filter rates, yields of wax, or oil content of the wax.

Following the completion of the first filtration the cold, wet wax cake was transferred to a wax washing tank. Cold solvent was charged into the slurry tank and the wax cake was reslurried. The resultant slurry was filtered. A yield of 31.1 weight per cent of purified wax containing 0.44 weight per cent oil was obtained. The wax was percolated through bauxite at F. to a yield of 25 barrels of wax per ton of bauxite to produce a finished wax with satisfactory color stability.

Although Stoddard Solvent has been mentioned specifically, it is clear that solvents which show a preferential solubility for oil over wax at a dewaxing temperature can be employed. Thus, solvents which can be used are those including acetone, methyl ethyl ketone, methyl isobutyl ketone, ethylene dichloride, methylene chloride, propane and the like.

Reasonable variation and some modification are possible within the scope of the foregoing disclosure and the appended claims to the invention the essence of which is found in the addition of at least one volume of solvent to ten volumes of wax-oil mixture to be deoiled when it is found to form lumps on cooling with slow agitation in the absence of solvent or in the presence of a very limited proportion of solvent all as set forth, described and aboveexemplified for the purpose of supplying a disclosure according to law.

I claim:

1. A process for deoiling a wax-oil distillate fraction boiling in the range 700850 F. and which forms crystalline wax lumps upon cooling although the oil, when said lumps are formed, is still of a viscosity sufficiently low to be stirred and chilled, said fraction containing from 20-50% of removable wax, which process comprises the steps of adding to said fraction while the wax is in solution, a naphtha fraction boiling in the range 200-400 F., the volume ratio of said naphtha fraction to said wax-oil distillate fraction being in the range 1:10 to 1:5, cooling the resulting mixture during slow agitation to obtain wax crystals without wax lump formation, and separating said wax crystals from said mixture.

2. Deoiling of a wax distillate fraction boiling in the range 650-850 F., obtained by distillation of a San Roque, Venezuela, crude oil, the said distillate forming wax lumps upon cooling, which comprises the steps of adding to said fraction one volume of a naphtha solvent,

boiling in the range ZOO-400 F., to each-five volumes of range 650850 F. and, having a viscosity of 388,138 at J 210 F., obtained by distillationtof. a-San Roque, Venezuela, crude oil, the said distillate formingwax lumps upon cooling, which comprises the, steps of adding to .said fractionone volume of anaphtha solvent, boilinginfthe range ZOO-400 F., to each five volumeszof saidtfraction at a temperature of about 140 F. and, then chilling the mixture at about 1 F. per minute; while slowly agitating it to effect precipitation, of. wax which occurs to a sub stantial extent when the temperature. has reached in. the neighborhood of 50 F.; adding 8 volumes ofsolvent at about 50 F to the slurry thus obtained; and thenfiltering the waxfrom-the oil and solvent mixture.

4. A deoilingprocess according to claim 1. wherein the naphtha is a crude-oilnaphthafraction and boils within the rangeGOO to 400 F.

5. The method for separating wax from a Wax-oilfraction whichboilswithinthe range 650-950? F. and;.contains from 2050%-of removable wax and which forms crystalline wax lumps upon cooling althoughth oil when said lumps are formed, is still of a viscosity 'sufiiciently low to'be stirred and chilled, whichprocess comprises adding to said wax-oil fraction, while the wax is in solution in the oil, from one volume of a solvent, which dissolves the oil but which doesnot substantially dissolve the wax at dewaxing temperature, to each ten volumes of wax-oil fraction to one volume of said solvent to each five volumes of said wax-oil fraction, and subsequently cooling the resulting mixture with slow agitation to obtain wax crystals without wax lump formation.

6. A process according to claim 5 wherein the solvent is a naphtha boiling in the range 200 to 400 F.

7-. A process according to claim 5 wherein the solvent is acetone.

8. A process according to claim 5 wherein the solvent is methyl ethyl ketone.

9. A process according to claim 5 wherein the solvent is methyl isobutyl ketone,

10. A process according to claim 5 wherein the solvent is ethylene dichloride.

11. A processaccording toclairnS wherein one volume of the solvent to each fiyevolumes ofrthe wax-oil fraction is added prior to wax crystal. formation and additional solvent is added subsequent to wax crystal formation.

References Cited in the tile of this patent UNITED STATES PATENTS Number Name Date 2,229,659 Carr ..Jan. 28, 1941 2,463,845 Backlund et a1. Mar. 8, 1949 2,484,728 Pattillo Oct. 11, 1949 2,625,502. Backlundet al ,Jan. 13, 1953 

1. A PROCESS FOR DEOILING A WAX-OIL DISTILLATE FRACTION BOILING IN THE RANGE 700-850* F. AND WHICH FORMS CRYSTALLINE WAX LUMPS UPON COOLING ALTHOUGH THE OIL, WHEN SAID LUMPS ARE FORMED, IS STILL OF A VISCOSITY SUFFICIENTLY LOW TO BE STIRRED AND CHILLED, SAID FRACTION CONTAINING FROM 20-50% OF REMOVABLE WAX, WHICH PROCESS COMPRISES THE STEPS OF ADDING TO SAID FRACTION WHILE THE WAX IS IN SOLUTION, A NAPHTHA FRACTION BOILING IN THE RANGE 200-400* F., THE VOLUME RATION OF SAID NAPHTHA FRACTION TO SAID WAX-OIL DISTILLATE FRACTION BEING IN THE RANGE 1:10 TO 1:5, COOLING THE RESULTING MIXTURE DURING SLOW AGITATION TO OBTAIN WAX CRYSTALS WITHOUT WAX LUMP FORMATION, AND SEPARATING SAID WAX CRYSTALS FROM SAID MIXTURE. 